No git clone for review-build-cng-env and review-deploy CI jobs

Context

#191273 (comment 1227409061)

From Draft to Ready

• Remove test commit (4612df3d)

What does this MR do?

• Adds tooling to download files/folders from repos
• Adds documentation about how to do this (see rendered markdown)
• Applies the tooling to review-build-cng-env and review-deploy CI jobs.

Results

git clone for both those jobs (and any other job really, as we download the same repo every time, different branches) is between 20 seconds and 30 seconds.

We should therefore save between 40 and 60 seconds on the critical path of review app deployments 🚀 (minus the time it takes to actually download the files (~1s in my tests)).

• review-build-cng-env job: https://gitlab.com/gitlab-org/gitlab/-/jobs/3673259700#L14
• review-deploy job: https://gitlab.com/gitlab-org/gitlab/-/jobs/3673259707#L15

Screenshots

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.